From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7D3FC433EF for ; Fri, 13 May 2022 14:33:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1381201AbiEMOdU (ORCPT ); Fri, 13 May 2022 10:33:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1380925AbiEMO3j (ORCPT ); Fri, 13 May 2022 10:29:39 -0400 Received: from mail-pl1-x629.google.com (mail-pl1-x629.google.com [IPv6:2607:f8b0:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F479941B2 for ; Fri, 13 May 2022 07:28:01 -0700 (PDT) Received: by mail-pl1-x629.google.com with SMTP id d22so8086977plr.9 for ; Fri, 13 May 2022 07:28:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=+QQdCynx9R6U6w/GBf0MKxMrNELH2gn+H5u0wn8VzXI=; b=qV51SP4bOcD0/cAU86xbrh+y3FdrsrCiQ/Bqp4lxWyyZjye8rk5+XElov551PASVRY D4ESwLtpEly+3JTdCMw99va5kEsNbH50qP3PhuThC3W4qFU0FjfCbTZ2jEd/xkEvfhzd xTe4pmEvx2R/9j+wbCJXDI9d3THSMLg2xlWA4VsLGVxhRr2uRRDbL3kPvt0dAU9WT5Iu JuiVzhfSCWcytG3zd7br6Gob8cSnaJyInz/2DsEMmzzcsE/P+2uhWz6w/ZD8JjGB+9w2 CCJo6kPnJSaLlVja/gYUUe7C9pYOKQoZAHtTb4vdtf5wfpNhYFESthNKiO+pc1yb80Br 7vdA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=+QQdCynx9R6U6w/GBf0MKxMrNELH2gn+H5u0wn8VzXI=; b=36KHjdDU4T5GEgBwz1Bo9dCYAINrtr59cEEeXHclg2eSa7DUwrVw3Ooj5/x768HlvL PWR/qghSASGy6kVUmYIflA85psWCmTf46jwzvGoTh41sOtAxws3+18Zov/JwMamQeEtO Ecng6rJunM5FXoWnOfvHw1dyzZfJWTaOGgxTXLkefC25GrnhJnBm2LQl2RmOsqrxay1+ uGYC+HyLQ10L/SqGhjNHCzQEaTTkpuhNpBkrWVUCTKEsR8EjyuqKUN3YVs4AndjxP981 M/677UjSgXmTCL4qtngWBVzMQDRIJQjXCdzXZPbi1SZNGuxMfmJdYdNCnWfRfn3deRCw w55A== X-Gm-Message-State: AOAM533qb502a2WD/d7kSRlQt7QvgbMIfxlxIinHdgyvEB6kndypldDb 5sssD31oY326V487J1cY7Y6OMQu/XeCIGQ== X-Google-Smtp-Source: ABdhPJyUkw0Dot81TbFysPPUNr3WVmg1+FbhuOz8hiv6Yq1uHVvAQecgrf+in/8vjWiDz1CBG7OujQ== X-Received: by 2002:a17:902:aa85:b0:155:ceb9:3710 with SMTP id d5-20020a170902aa8500b00155ceb93710mr4874209plr.59.1652452080864; Fri, 13 May 2022 07:28:00 -0700 (PDT) Received: from localhost ([139.177.225.250]) by smtp.gmail.com with ESMTPSA id j16-20020a634a50000000b003c14af50639sm1650442pgl.81.2022.05.13.07.27.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 May 2022 07:28:00 -0700 (PDT) Date: Fri, 13 May 2022 22:27:47 +0800 From: Muchun Song To: David Laight Cc: 'Andrew Morton' , liqiong , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm: change "char *bdi_unknown_name" to "char bdi_unknown_name[]" Message-ID: References: <20220512082637.24649-1-liqiong@nfschina.com> <20220512130051.94a0c53e5d1498292473975d@linux-foundation.org> <4b21dec7e98243b89daea96286c33434@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4b21dec7e98243b89daea96286c33434@AcuMS.aculab.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 13, 2022 at 11:06:23AM +0000, David Laight wrote: > From: Andrew Morton > > Sent: 12 May 2022 21:01 > > > > On Thu, 12 May 2022 16:26:37 +0800 liqiong wrote: > > > > > "char bdi_unknown_nam[]" string form declares a single variable. > > > It is better then "char *bdi_unknown_name" which creates two > > > variables. > > > > > > ... > > > > > > --- a/mm/backing-dev.c > > > +++ b/mm/backing-dev.c > > > @@ -20,7 +20,7 @@ struct backing_dev_info noop_backing_dev_info; > > > EXPORT_SYMBOL_GPL(noop_backing_dev_info); > > > > > > static struct class *bdi_class; > > > -static const char *bdi_unknown_name = "(unknown)"; > > > +static const char bdi_unknown_name[] = "(unknown)"; > > > > > > > heh, fun patch. We actually do this quite a lot. > > > > grep -r "^[a-z].*char \*[a-z].*= \"" . > > > > is a pathetic pattern which catches a lot of them. > > > > > > However. I expected your patch to shrink the kernel a bit, but it has > > the opposite effect: > > > > hp2:/usr/src/25> size mm/backing-dev.o > > text data bss dec hex filename > > 21288 9396 3808 34492 86bc mm/backing-dev.o-before > > 21300 9428 3808 34536 86e8 mm/backing-dev.o-after > > > > Even .data became larger. I didn't investigate why. > > The linker can merge replicated strings > (ie data in .rodata.str1.n sections) > but I don't think the compiler puts variables into that section. > > So if you have: > static const char *const foo_xxx = "foo"; > in multiple source/object files you get lots of pointers > but only one string. > OTOH with: > static const char foo_xxx[] = "foo"; > you get lots of copies of the string. > Which is smaller depends on the number of variables and the length > of the string. > Good point. I have searched the whole code. There are 19 places where use the string "(unknown)". Seems it is better to drop this change. arch/mips/alchemy/devboards/db1xxx.c:48: return "(unknown)"; drivers/acpi/device_pm.c:44: return "(unknown)"; drivers/base/component.c:101: component ? dev_name(component->dev) : "(unknown)", drivers/block/rbd.c:5137: spec->image_id, spec->image_name ?: "(unknown)", drivers/gpu/drm/i915/display/intel_dsi_vbt.c:570: return "(unknown)"; drivers/i3c/master/mipi-i3c-hci/ext_caps.c:50: "(unknown)", "master only", "target only", drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil.c:85: return "(unknown)"; drivers/platform/x86/thinkpad_acpi.c:7506: thinkpad_id.ec_version_str : "(unknown)"); drivers/usb/gadget/udc/omap_udc.c:2800: type = "(unknown)"; fs/cifs/cifs_swn.c:653: seq_puts(m, "(unknown)"); fs/cifs/cifsfs.c:434: seq_puts(s, "(unknown)"); fs/ext4/super.c:835: path = "(unknown)"; include/drm/drm_mode_object.h:118: return "(unknown)"; \ lib/error-inject.c:187: return "(unknown)"; mm/backing-dev.c:23:static const char *bdi_unknown_name = "(unknown)"; mm/filemap.c:3664: path = "(unknown)"; net/ipv4/cipso_ipv4.c:444: type_str = "(unknown)"; net/ipv6/calipso.c:384: type_str = "(unknown)"; sound/firewire/dice/dice-proc.c:35: return "(unknown)"; Thanks.